The present embodiments relate to a magnetic resonance apparatus including receive coils and a receiver device for processing magnetic resonance signals received by coil elements of the receive coils.
In magnetic resonance imaging (MRI), nuclear spins are excited by a radio-frequency field of a transmit coil. Magnetic resonance signals that are emitted by the nuclear spins may be captured by a receive coil and evaluated in order to calculate magnetic resonance images. In such applications, magnetic resonance coils may also be embodied simultaneously as transmit coil and as receive coil.
In situations where magnetic resonance images having a high signal-to-noise ratio are to be acquired, coil elements referred to as “local coils” (e.g., antenna systems that are arranged directly on the object (a patient) that is to be scanned) may be used in MRI. Local coils may be positioned on the patient (e.g., anterior arrangement) or under the patient (e.g., posterior arrangement). If a magnetic resonance measurement is to be performed, the excited nuclei induce a voltage (e.g., the magnetic resonance signal) in the individual coil elements of the local coil. The magnetic resonance signal is amplified by a low-noise preamplifier (LNA) and forwarded to a receiver device (e.g., receive electronics). The signal-to-noise ratio may be improved by using strong static magnetic fields (e.g., in the range from 1.5 T to 12 T).
In such applications, the coil elements of the local coils may be embodied as very small, since this also improves the signal-to-noise ratio. Accelerated measurement methods, in which k-space undersampling is performed, for example, within the framework of parallel imaging, have also been proposed. For these reasons, very dense arrays of coil elements have been proposed. The coil elements may have completely different orientations relative to the transmit field. A plurality of transmission channels or transmission options may be used in order to enable this large number of coil elements to be read out. This transmission may take place by way of a hardwired communications link (e.g., a coaxial cable) In this case, a switching device may be provided if the number of coil elements exceeds the number of input channels provided on the receiver device side.
The high numbers of channels to be transmitted and the high dynamics of magnetic resonance imaging make it difficult to implement wireless receive coils (e.g., wireless local coils). Wireless local coils have a plurality of advantages. In addition to a positive marketing effect, wireless local coils have a significant advantage in terms of workflow and in patient comfort owing to the absence of cables. This applies, for example, since in magnetic resonance technology, the cables are to be provided with devices known as standing wave traps that are intended to prevent danger to patients caused by common-mode currents on the sheaths of the coaxial cables. The standing wave traps make the cables thick and heavy.
Cableless local coils, which accordingly operate using a wireless communications link, have already been proposed in principle. Solutions, in which along the lines of MIMO technology, signals of a plurality of coil elements may also be transmitted collectively, are known (cf., DE 10 2007 047 020 A1). However, an approach of this kind may no longer be implemented in the case of a digitization of the magnetic resonance signals on the receive coil side, as has been proposed more frequently in recent times. If the magnetic resonance signals are already digitized on the receive coil side, a separate transmit channel for wireless transmission is to be made available for each coil element having magnetic resonance signals that are to be transmitted.